For progress in microelectronics, it is important to have tools for inspecting microelectronical structures on a chip or wafer with ever increasing spatial resolution. At the same time, it is important to decrease the costs of such inspections in order for the industry to fabricate devices of ever increasing complexity at low costs.
Technologies such as microelectronics, micromechanics and biotechnology have created a high demand for structuring and probing specimens within the nanometer scale. Micrometer and nanometer scale process control, inspection or structuring, is often done with charged particle beams, e.g., probing or structuring is often performed with charged particle beams which are generated and focused in charged particle beam devices. Charged particle beams offer superior spatial resolution compared to photon beams, due to their short wave lengths at comparable particle energy.
Due to the progressing miniaturization of integrated circuits, it has become important to study, for example, the cross-section, the crystal structure and the layer structure of an integrated circuit structure below the surface of the wafer. This can done by inspecting a cross sectional thin slice (membrane) from the wafer or chip by means of a transmission electron microscope (TEM). Despite the progress in TEM sample preparation and TEM inspection, it is still complicated, expensive and time-consuming to carry out a TEM inspection because of the many steps needed for each measurement. For these reasons, inspections of cross sectional thin slices of a specimen, in particular the inspection of membranes of a wafer or chip, are expensive. Cross sectional inspections for a failure analysis of integrated circuits on a regular basis are therefore difficult.
Another prominent tool for inspections is the scanning electron microscope (SEM). The SEM uses a primary electron beam as a means to probe the surface structure of a given specimen. An interaction of the primary electron beam with the specimen causes electrons to be released into a backward direction with respect to the primary electron beam where they are detected by an electron detector. By scanning the primary electron beam across the specimen and determining the rate of the released electrons at each scan position, an image of the surface of the specimen with high spatial resolution is obtained. The spatial resolution of the image is essentially given by the size of the beam focus.
For inspections of cross sections, layer structures and crystal structures with an SEM, problems in light of a small material contrast and sample charging may occur. There are several methods for preparing a specimen to be able to provide cross-sectional images. These sample preparation methods are commonly conducted separately from the manufacturing processes of the specimen and are, thus, time consuming. Low voltage imaging for a reduction of specimen charging can generally not be simultaneously provided for all materials of a specimen.